What is email A/B testing?

Email A/B testing

You have a hunch that a different subject line might get more opens. Or maybe you're wondering if that bright orange button would outperform the subtle gray one. A/B testing turns those hunches into answers.

Email A/B testing compares two versions of the same email to see which performs better. You change one element, send each version to a portion of your list, and let the data tell you what works. The winning version goes to everyone else.

Why A/B testing matters for email marketers

Every audience is different. What works for one brand's subscribers might fall flat with yours. A/B testing builds a playbook based on your actual customers, not industry averages or borrowed best practices.

The benefits compound over time. Each test teaches you something about your audience's preferences, and string enough tests together, you'll understand exactly what makes your subscribers click, open, and buy.

Testing also removes the guesswork from team debates. Instead of arguing over whether emojis belong in subject lines, you run a test and let the results settle it.

What you can test in your emails

If you can change it, you can test it. Here are the elements that tend to move the needle most:

Subject lines directly impact whether anyone sees your email at all. Test length, tone, personalization, urgency language, or questions versus statements.

Preview text works alongside your subject line in the inbox. A compelling preview can boost opens even when the subject line stays the same.

Sender name shapes first impressions. Try your company name versus a person's name, or test different team members to see who earns more trust.

Email design covers everything from layout to images to color schemes. Some audiences prefer minimal designs while others respond to rich visuals.

Call-to-action buttons deserve special attention since they drive clicks. Test button color, size, copy, and placement within the email.

Send timing can dramatically affect engagement. The best time to reach your audience might surprise you.

How to run an effective A/B test

Start with a clear hypothesis. "I think adding the subscriber's first name to the subject line will increase opens because it feels more personal." This keeps your test focused and your results meaningful.

Change only one variable per test. If you swap the subject line and the CTA button at the same time, you won't know which change drove the results. Isolate your variables to get clean insights.

Use a large enough sample. Small audiences can produce misleading results. Most platforms recommend at least 1,000 subscribers per variation to reach statistical significance. If your list is smaller, run a 50/50 split and apply what you learn to future campaigns.

Give the test enough time. People don't check email instantly. Wait at least 24 hours before declaring a winner, and longer if you're measuring clicks or conversions rather than opens.

Match your metric to your variable. Testing subject lines? Measure open rates. Testing CTA buttons? Track click-through rates. Testing product recommendations? Look at conversions.

Ready to start testing? ActiveCampaign's split testing tools let you test subject lines, email content, and send times with automatic winner selection.

Common A/B testing mistakes to avoid

Testing too many things at once tops the list. Multivariate testing exists, but it requires massive audiences to produce reliable results. Stick to one variable until you've mastered the basics.

Ending tests too early leads to false conclusions. Early results often flip as more data comes in. Set your test duration before you start and resist the urge to peek and declare victory.

Ignoring statistical significance means acting on noise rather than signal. A 2% difference between versions might just be random variation. Look for clear winners with meaningful gaps before changing your strategy.

Forgetting to document results wastes your hard work. Keep a log of every test, including your hypothesis, what you tested, the results, and what you learned. This becomes your brand's email intelligence database.

A/B testing ideas to try first

If you're new to testing, start with subject lines. They're easy to create, quick to test, and directly impact your most visible metric.

Try these subject line tests:

• Short versus long
• Question versus statement
• With personalization versus without
• Urgency language versus benefit-focused language

Once you've optimized your subject lines, move to email content and design. Test whether your audience prefers image-heavy emails or text-focused ones, and see if a single CTA outperforms multiple options.

For automated email sequences, test timing between messages. Does your welcome series perform better when the second email arrives after one day or three days?

FAQs

How long should I run an A/B test?
At minimum, 24 hours for open rate tests and 48-72 hours for click or conversion tests. Longer is better if you have the patience.

What's a good sample size for email A/B testing?
Aim for at least 1,000 subscribers per variation. Smaller lists can still test, but treat results as directional rather than definitive.

Should I A/B test every email I send?
Focus on emails you send frequently, like newsletters or automated sequences. One-time campaigns to small segments won't give you reusable insights.

What if my test results are inconclusive?
That's useful information too. It means your audience doesn't have a strong preference between the options, so you can move on to testing something else.

Want to see what resonates with your subscribers? Start your free ActiveCampaign trial and run your first A/B test today.